The present invention relates to a roller bearing for an endless linear motion in which a casing mounted on a linear track can make an endless linear motion through a plurality of rollers circulating endlessly, and relates in particular to a shape of the wall surfaces of a direction changing path of the rollers installed at the front and rear ends of the casing of the roller bearing for an endless linear motion. The purpose of the invention is to provide a cross-sectional shape of a direction changing path which will not unnecessarily increase the resistance of the rollers. The direction change path semicircularly connects the ends of a load track which is a load zone and a return hole which is a no load zone, and allows a smooth direction changing motion of the rollers. The load track and the return hole are straight paths, are parallel to each other and are in symmetry with respect to a plane.
An embodiment of the roller bearing for endless linear motion has a construction such as shown in FIGS. 2 and 3. In this embodiment, a casing 2 mounted on a track rail 1 having a linear shape makes an endless linear motion through a plurality of rollers circulating endlessly. The endless circulating path of roller 3 consists of a load track 4 and a return hole 5, both being straight and parallel to each other, and direction changing paths 6 which connect both ends of said load track 4 and said return hole 5 and allow a smooth direction changing motion of the rollers. The load track 4, return hole 5 and direction changing path 6 all have an approximately square cross section, the length of one side thereof being approximately a. The center lines joining the centers of the approximately square cross section of said load track 4, return hole 5 and direction changing path 6 all lie on a same plane which is a center plane 12 (FIG. 1). The shape of the roller 3 is such that, the dimensions of its height and diameter are approximately a.
The load track 4 is formed from a right angle V groove 7 on the casing 2 and a right angle V groove 8 on the track rail 1. The return hole 5 is provided inside the casing 2. The direction changing path 6, is formed in side plate 9 provided respectively at the front and rear ends of the casing 2.
As shown in FIG. 1, the load track 4 and return hole 5 are in symmetry to each other with respect to a perpendicular bisecting plane 13 of a center plane 20 which passes through centers 10, 11 of the rollers rolling respectively in the load track 4 and the return hole, both being linear paths. The direction changing path 6 is a semicircular arc having its center on said center plane 20 so as to connect both ends of the load track and return hole, and the axis of revolution of the direction changing path is the perpendicular bisecting line 13 (in FIG. 1, the perpendicular bisecting line shown same to the perpendicular bisecting plane) which is an intersecting line produced between a plane perpendicular to the center plane at both ends of the load track 4 and the return hole 5, and said perpendicular bisecting plane 13.
Accordingly, as shown in FIG. 26, the four wall surfaces of the direction changing path 6 are formed basically of surfaces encompassed by inner and outer conical surfaces 16, 17 and 18, 19, respectively, which are orthogonal to each other, respectively, and which are respectively a distance a/2 away from conical surfaces which pass through the centers 10, 11 respectively and have apex at 14, 15 respectively which are intersections of perpendicular bisectors of the respective sides of the square cross sections of the load track 4 and return hole 5 (intersections 14, 15 both lie on the perpendicular bisecting line 13). Among the four wall surfaces of the direction changing path, the inner wall surfaces will be designated as 6a, 6b, and the outer wall surfaces will be designated as 6c, 6d. Further, in FIG. 1, the center plane 20 is shown as a center line 12 joining the centers 10, 11.
As described previously, the diameter and height of the roller 3 are both a, and the cross section taken along the axis of the roller 3 is a square having a side length a. Therefore, both the load track 4 and return hole 5 have a cross-sectional shape which is a square with a side length slightly larger than a so as to allow the roller 3 to roll through. However, when attempt is made to allow the rolling of the roller 3 in a direction changing motion, if the direction changing path has a cross-sectional shape which is a same size as the load track 4 and return hole 5, the roller 3 will become incapable to roll. Further details regarding this point will become clear from the descriptions to be made hereinafter.
In the prior art, the cross-sectional shape of the direction changing path 6 was, in order for the rollers to roll while making a directional change, a square shape having a side length a+X which was considerably larger than the side length of a square section of the load track 4 and return hole 5. Namely, the distance between wall surfaces 6a and 6d and the distance between wall surfaces 6b and 6c was a+X.
The just described direction changing path having an enlarged square cross section resulted in a too large play for the rollers rolling inside said direction changing path. The too large play was the main cause of the so-called "stick-slip" motion and increased the resistance inside the direction changing path. In other words this was one of the causes which increased the resistance of the roller bearing for an endless linear motion as a whole.
The present invention aims to provide a direction changing path of a roller bearing for an endless linear motion in which there will be a less sliding resistance, and in which there will be a smooth direction change of the rollers rolling therein.
The construction of the present invention is as described in the claims. There is provided a direction changing path for the rollers of a roller bearing for an endless linear motion which allows an endless linear motion of a casing mounted on a track rail through endlessly circulating cylindrical rollers. The direction changing path allows the rollers in a load track to make a rolling motion up to a return hole located in a no load zone while making a directional change. The direction changing paths are provided at both the front and rear ends of the casing of the roller bearing. The outer wall surface of said direction changing path is formed by a curved surface of a spherical band which is convex outward with a fixed curvature. As a result, as regards the rollers rolling inside the direction changing path, any roller which axis is directed 90 degrees differently from another roller can have a minimum clearance with the wall surfaces. This assures a smooth direction changing motion and the resistance between the rollers and the direction changing path will become less, thus, the resistance of the roller bearing for an endless linear motion as a whole is reduced. Also, since there is less play the locus of the rollers inside the direction changing path will become more definite. Thus, it becomes possible to accurately determine the number of rollers to be accommodated inside an endlessly circulating path. Accordingly, since the amount of clearance in the row of the rollers can be set to a minimum, it became possible to produce a superior effect such as to essentially improve the load capacity of the roller bearing for an endless linear motion.